The present invention relates to a packing material for chromatographic separations and to a method of manufacturing the same. More particularly, the present invention relates to a packing material for liquid chromatography produced by mixing a carbon product, such as carbon black with a synthetic resin and/or a pitch component, granulating the mixture, and heat treating the resultant granules. The present invention also relates to methods of chromatographic separation that employ the granules.
Conventionally, packing materials for liquid chromatography have included silica gel materials and synthetic resin-based materials. However, problems such as chemical stability, including solubility, have resulted in silica gel-based materials exhibiting poor durability as a packing material.
In chromatography and other separation methods, there is a certain amount of selectivity that is necessary in order for the stationary phase to separate the various components in a mixture. For this reason, carbon products, such as carbon black, have not been used as a standard stationary phase in separation systems because carbon is a strong non-specific adsorbent. This has been disappointing in the past, because carbon products, otherwise, would have many advantages over commercially available adsorbents. For instance, there are no corrosion problems with carbon products nor are there any swelling problems with carbon products. In addition, carbon products can be subjected to large temperature ranges and/or extreme pressures which would be beneficial for certain types of adsorptions, such as temperature swings used in some types of chromatography. In addition, with certain separation processes used in the production of biopharmaceuticals for clinical applications, the sterilization requirements or recommendations provide for the use of hot sodium hydroxide. With such sterilization procedures, the current separation devices such as silica columns, cannot be used. Further, the polymeric columns such as cellulose polymers, are chemically but not physically stable to such sterilization treatments.
U.S. Pat. No. 5,270,280 relates to the use of carbon black packing materials for liquid chromatography, wherein the carbon blacks have specific dimensional ratios, specific particle diameters and surface areas, and specific micropore volumes. The patent is incorporated herein in its entirety by reference. The methods of making the packing material according to U.S. Pat. No. 5,270,280 include granulating a carbon black-containing mixture and heat-treating the granules at a high temperature in the range of from 800xc2x0 C. to about 3000xc2x0 C., in an inert atmosphere. The high temperature heat-treatment is most likely necessary to carbonize and graphitize the binder material in order to form a graphitic layer. According to the patent, if the temperature is below 800xc2x0 C., the graphitization of the binder is not sufficient, resulting in the packing material having insufficient strength. While the patent describes the packing material as providing improved mechanical durability and separating characteristics, a need still exists for an improved liquid chromatography packing material that has improved mechanical durability and improved separating properties.
It is desired to provide an improved liquid chromatographic packing material and a method of producing such a material which does not require a high temperature heat-treatment or graphitization step.
In addition, it is desired to provide a method of chromatographic separation that provides improved separation of sample components.
The present invention relates to an improved chromatographic packing material made of carbonaceous particle-containing granules preferably having at least one organic group attached thereto. The granules include carbonaceous particles and the carbonized product of a carbonizable synthetic resin, pitch component, or both. Preferred granules include carbon black particles having attached organic groups and a carbonized synthetic resin, pitch component, or both.
The present invention further relates to a process for making the packing material of the present invention and includes: mixing carbonaceous particles with at least one synthetic resin, pitch component, or both, and with at least one organic or aqueous solvent, to form a mixture; granulating the mixture to form granules; heating the granules at a relatively low temperature of from about 400xc2x0 C. to less than 800xc2x0 C. to carbonize the synthetic resin, pitch component, or both, and to evaporate the solvent. Once formed, the packing material can be further customized for specific uses by attaching an organic group or groups to the carbon surface.
The carbonized synthetic resin, pitch component, or both, preferably acts to strongly bind the carbonaceous particles into a strong granule, very differently than the temporary binding action of pelletizing or binding agents designed to facilitate ready dispersal of carbon black particles from a pelletized carbon black.
The packing materials of the present invention preferably exhibit excellent mechanical durability and preferably provide improved separating abilities in chromatographic separation applications. The surface-modified granular packing materials of the present invention are particularly useful in liquid chromatographic separation applications.
Additional features and advantages of the present invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the description and appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.